Methods and devices for detecting nitrogen oxides

Abstract

A method for detecting nitrogen oxides, the method comprising monitoring the change in potential difference between a working electrode and a reference electrode as the working electrode is exposed to nitrogen oxides, where the working electrode includes an inorganic non-metallic oxide selected from spinel-structured compounds and wolframite-structured compounds, and where the working electrode and the reference electrode are in contact with a solid electrolyte.

What is claimed is: 
     
         1 . A method for detecting nitrogen oxides, the method comprising:
 monitoring the change in potential difference between a working electrode and a reference electrode as the working electrode is exposed to nitrogen oxides, where the working electrode includes an inorganic non-metallic oxide selected from spinel-structured compounds and wolframite-structured compounds, and where the working electrode and the reference electrode are in contact with a solid electrolyte.   
     
     
         2 . The method of the preceding claim, where the working electrode includes a ferrite. 
     
     
         3 . The method of any one of the preceding claims, where the working layer includes a tungstate. 
     
     
         4 . The method of any one of the preceding claims, where the solid electrolyte is a superionic oxide ion conducting ceramic. 
     
     
         5 . The method of any one of the preceding claims, where the solid electrolyte is yttria stabilized zirconia. 
     
     
         6 . The method of any one of the preceding claims, where the working electrode includes a dopant. 
     
     
         7 . The method of any one of the preceding claims, where the inorganic non-metallic oxide is in the form of particulate having an average particle size of from 10 to 1000 microns. 
     
     
         8 . The method of any one of the preceding claims, where the working electrode includes nickel ferrite. 
     
     
         9 . The method of any one of the preceding claims, where, in the absence of nitrogen oxides, the potential difference between the working electrode and the reference electrode is from about 25 to about 250 millivolts. 
     
     
         10 . The method of any one of the preceding claims, where the nitrogen oxides are NOx. 
     
     
         11 . A sensor for detecting nitrogen oxides comprising:
 a solid electrolyte;   a working electrode disposed on said solid electrolyte, where the working electrode includes a spinel structured compound or a wolframite structured compound;   a reference electrode disposed on and in electrical communication with said electrolyte;   an ohmic contact in electrical communication with the working electrode; and   an electrical detection device that can detect the potential difference between the reference electrode and the working electrode.   
     
     
         12 . The sensor of the preceding claim, further comprising a heating device in thermal communication with the electrolyte. 
     
     
         13 . The sensor of any one of the preceding claims, further comprising a temperature measuring device in thermal communication with said electrolyte, said heating device, or both said electrolyte and said heating device. 
     
     
         14 . The sensor of any one of the preceding claims, where the working electrode includes a spinel structured compound and the spinel structured compound is a ferrite. 
     
     
         15 . The sensor of any one of the preceding claims, where the working electrode includes a wolframite structured compound and the wolframite structured compound is a tungstate. 
     
     
         16 . The sensor of any one of the preceding claims, where the spinel structured compound is nickel ferrite. 
     
     
         17 . The sensor of any one of the preceding claims, where the spinel structured compound or the wolframite structured compound is in the form of particles having an average particle size of from 10 to about 1000 microns. 
     
     
         18 . The sensor of any one of the preceding claims, where the thickness of the working electrode is less than 1000 microns. 
     
     
         19 . The sensor of any one of the preceding claims, where the thickness of the working electrode is less than about 100 microns. 
     
     
         20 . The sensor of any one of the preceding claims, where the electrolyte is a superionic oxide ion conducting ceramic material. 
     
     
         21 . A vehicle comprising:
 an engine; and   a sensor for detecting nitrogen oxides produced by said engine, the sensor including a solid electrolyte; a working electrode disposed on said electrolyte, where the working electrode includes a spinel structured compound or a wolframite structured compound; a reference electrode disposed on said electrolyte, an ohmic contact disposed said working electrode; and an electrical detection device that can detect the potential difference between the reference electrode and the working electrode.   
     
     
         22 . The vehicle of the preceding claim, where the engine is a reciprocating engine. 
     
     
         23 . The vehicle of any of the preceding claims, where the engine is a diesel engine. 
     
     
         24 . The vehicle of any of the preceding claims, where the engine is a turbine engine. 
     
     
         25 . The vehicle of any of the preceding claims, where the sensor is positioned within the exhaust stream exiting the engine. 
     
     
         26 . The method of any of the preceding claims, where the reference electrode includes a noble metal. 
     
     
         27 . The sensor of any of the preceding claims, where the reference electrode includes a noble metal. 
     
     
         28 . The vehicle of any of the preceding claims, where the reference electrode includes a noble metal.